Iwan Rheon was born in Carmarthen and moved to Cardiff with his family at age five. Participation in the National Eisteddfod of Wales led to him being cast, while in his final year at school, in Welshlanguage soap opera Pobol Y Cwm.

He went on to train at the London Academy of Music and Dramatic Art (LAMDA). After graduating in 2008, Iwan made his stage debut in Eight Miles High at the Royal Court, Liverpool. Following this, he quickly landed his breakthrough role as the haunted, suicidal Moritz in the musical version of Franz Wederkind's Spring Awakening, for which he won the 2010 Olivier Award for Best Supporting Actor in a Musical.

In 2009, Iwan joined the cast of E4's BAFTA award-winning superhero drama, Misfits, alongside Robert Sheehan, Lauren Socha, Nathan Stewart-Jarrett and Antonia Thomas. The series centered on a group of teenage delinquents who acquired superhuman powers after a mysterious storm. Iwan played Simon Bellamy in the first three series. To date, Misfits has been sold to over 100 territories, including the U.S., Latin America, Spain, Singapore, Russia, Kazakhstan, Italy, Scandinavia and Israel.

In 2010, Iwan returned to the stage in the National Theatre Wales' production of John Osborne's The Devil Inside Him.

Iwan went onto star in Remembrance Day, from Latvian playwright Aleksey Scherbak at The Royal Court Theatre. Looking at the politically charged tensions in modern day Latvia, Remembrance Day was developed from Royal Court workshops in Moscow in 2008 and 2009. The cast included Ruby Bentall, Michelle Fairley and Luke Norris.

Following this, Iwan made his cinematic debut in Resistance, a 2011 Welsh film based on the novel of the same name by Owen Sheers. After all the women in a remote valley on the Welsh border awaken to find their husbands have left to serve in the covert British Resistance, German occupiers arrive in this alternate-reality thriller set in 1944 where D-Day has failed and the United Kingdom has been invaded by Nazi Germany. Iwan starred alongside Andrea Riseborough and Michael Sheen.

In March 2012, Iwan appeared in Dexter Fletcher's Wild Bill, starring Charlie Creed-Miles, Will Poulter and Andy Serkis.

In 2013, Iwan was seen in British crime drama The Rise (Wasteland), alongside Timothy Spall, Luke Treadaway and Matthew Lewis. He also appeared in Spanish-Venezuelan historical drama film The Liberator, starring Édgar Ramírez.

2013 also saw Iwan join the cast of ITV's studio sitcom Vicious. Iwan starred alongside respected luminaries of British stage and screen, Ian McKellen, Derek Jacobi and Frances de la Tour. The show was written by Gary Janetti, the Emmy-nominated writer/producer behind hit shows Family Guy and Will & Grace. Vicious told the story of aging partners, Freddie (Ian McKellen) and Stuart (Derek Jacobi), two men who have lived together in a small London flat for nearly 50 years, whose worlds are turned upside down with the arrival of a young man, Ash (Iwan), as their new upstairs neighbor. The hit comedy returned for a second series in 2015.

In 2014, Iwan starred in BBC One's hugely popular five-part series Our Girl. The series followed 2013's highly successful single drama, which drew a consolidated audience of 6.3 million and received a nomination at the RTS Awards for Best Single Drama. Iwan played Smurf a soldier in the Royal Army Medical Corps alongside Lacey Turner and Ben Aldridge.

In 2015, Iwan starred in Netflix's original British mini-series, Residue, a futuristic sci-fi thriller, which was centered around the life of a photo-journalist after a mysterious explosion in the city centre of a dystopian metropolis. Iwan appeared opposite Natalia Tena. He was also seen in Charlotte's Song, a homage to Hans Christian Andersen's The Little Mermaid.

Iwan is known for his performance in the global phenomenon Game of Thrones, an original series based on George R.R. Martin's best-selling A Song of Ice and Fire series of fantasy novels. Created by show runners David Benioff and D. B. Weiss, it premiered on HBO in the United States in April 2011. Game of Thrones has attracted record numbers of viewers on HBO (U.S.) and Sky Atlantic (U.K.), and attained an exceptionally broad and active international fan base. The series has received widespread critical acclaim and has won 26 Primetime Emmy Awards, including the Primetime Emmy Award for Outstanding Drama Series in 2015 – when it set a record for the most wins for a series in a single year. Iwan joined the show in its third series as the sadistic Ramsay Bolton, formerly known as Ramsay Snow. Ramsay was the bastard son of Lord Roose Bolton, who became legitimized by the crown, thus making Ramsay lawful heir to Winterfell and the North. Game of Thrones's total number of awards now stands at a record 28, after last year's Emmy Awards win. It has also been nominated for Best Drama Series at the Critics' Choice Awards.

Iwan was recently seen in Aberfan: The Green Hollow on BBC One Wales. Aberfan: The Green Hollow is a 60-minute film-poem written by award-winning poet, novelist and playwright Owen Sheers, and directed by Pip Broughton. The film uses verse, imagery and music to explore the radical differences of the village before the Aberfan disaster, highlighting the strength of the community today.

Iwan is also known for his role in Christian Pasquariello's debut feature SUM1 about a young soldier stationed in a desolate forest while the remnants of humanity hide underground from alien invaders.

Iwan recently played Adolf Hitler in Adolf The Artist, in Sky One's satirical drama series Urban Myths. Iwan starred alongside Rupert Grint. The drama told the little-known tale of a young Adolf, before politics and before war, when all he could dream about was becoming a famous painter.

Iwan will be seen in Beth LaMure's indie drama Daisy Winters, alongside Carrie Preston and Brooke Shields, about an eleven-year-old girl's unconventional, yet deeply loving, relationship with her mother and what happens when this bond is harshly broken.

Iwan will next be seen starring in Sky Atlantic's new thriller Riviera, alongside Adrian Lester and Julia Stiles. The thriller follows the moral descent of an American art dealer whose life is shattered when her billionaire husband is killed in mysterious circumstances.

Iwan will be taking the lead in ABC's new drama Marvel's Inhumans. Marvel's Inhumans follows a race of superhumans with diverse and unique powers and explores the untold epic adventure of Black Bolt and the royal family. Iwan will star as Maximus, a charming Inhuman who is wholly devoted to the people of Attilan and his own brother, Black Bolt, despite craving the crown his sibling wears.

Iwan is also a talented singer song-writer. Last year, Iwan released his first album, Dinard following a series of well-received EPs – Tongue Tied, Changing Times, and Bang! Bang!